6 files changed, 40 insertions, 10 deletions
diff --git a/image/IDecodingTask.cpp b/image/IDecodingTask.cpp
index a067e7a7d..6e2f039be 100644
--- a/image/IDecodingTask.cpp
+++ b/image/IDecodingTask.cpp
@@ -142,8 +142,10 @@ MetadataDecodingTask::Run()
 // AnonymousDecodingTask implementation.
 ///////////////////////////////////////////////////////////////////////////////
 
-AnonymousDecodingTask::AnonymousDecodingTask(NotNull<Decoder*> aDecoder)
+AnonymousDecodingTask::AnonymousDecodingTask(NotNull<Decoder*> aDecoder,
+                                             bool aResumable)
   : mDecoder(aDecoder)
+  , mResumable(aResumable)
 { }
 
 void
@@ -168,5 +170,16 @@ AnonymousDecodingTask::Run()
   }
 }
 
+void
+AnonymousDecodingTask::Resume()
+{
+  // Anonymous decoders normally get all their data at once. We have some situations
+  // where they don't. If explicitly requested, resuming should be supported.
+  if (mResumable) {
+    RefPtr<AnonymousDecodingTask> self(this);
+    NS_DispatchToMainThread(NS_NewRunnableFunction([self]() -> void { self->Run(); }));
+  }
+}
+
 } // namespace image
 } // namespace mozilla
diff --git a/image/IDecodingTask.h b/image/IDecodingTask.h
index 196ce5fdc..3cbab5006 100644
--- a/image/IDecodingTask.h
+++ b/image/IDecodingTask.h
@@ -102,22 +102,20 @@ class AnonymousDecodingTask final : public IDecodingTask
 public:
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(AnonymousDecodingTask, override)
 
-  explicit AnonymousDecodingTask(NotNull<Decoder*> aDecoder);
+  explicit AnonymousDecodingTask(NotNull<Decoder*> aDecoder, bool aResumable);
 
   void Run() override;
 
   bool ShouldPreferSyncRun() const override { return true; }
   TaskPriority Priority() const override { return TaskPriority::eLow; }
 
-  // Anonymous decoders normally get all their data at once. We have tests where
-  // they don't; in these situations, the test re-runs them manually. So no
-  // matter what, we don't want to resume by posting a task to the DecodePool.
-  void Resume() override { }
+  void Resume() override;
 
 private:
   virtual ~AnonymousDecodingTask() { }
 
   NotNull<RefPtr<Decoder>> mDecoder;
+  bool mResumable;
 };
 
 } // namespace image
diff --git a/image/ImageOps.cpp b/image/ImageOps.cpp
index addee7f15..ddd2f200e 100644
--- a/image/ImageOps.cpp
+++ b/image/ImageOps.cpp
@@ -126,7 +126,7 @@ ImageOps::DecodeToSurface(nsIInputStream* aInputStream,
   }
 
   // Run the decoder synchronously.
-  RefPtr<IDecodingTask> task = new AnonymousDecodingTask(WrapNotNull(decoder));
+  RefPtr<IDecodingTask> task = new AnonymousDecodingTask(WrapNotNull(decoder), /* aResumable */ false);
   task->Run();
   if (!decoder->GetDecodeDone() || decoder->HasError()) {
     return nullptr;
diff --git a/image/SourceBuffer.cpp b/image/SourceBuffer.cpp
index de0719d45..de066e29f 100644
--- a/image/SourceBuffer.cpp
+++ b/image/SourceBuffer.cpp
@@ -451,10 +451,18 @@ SourceBuffer::AppendFromInputStream(nsIInputStream* aInputStream,
   uint32_t bytesRead;
   nsresult rv = aInputStream->ReadSegments(AppendToSourceBuffer, this,
                                            aCount, &bytesRead);
-  if (!NS_WARN_IF(NS_FAILED(rv))) {
-    MOZ_ASSERT(bytesRead == aCount,
-               "AppendToSourceBuffer should consume everything");
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (bytesRead == 0) {
+    // The loading of the image has been canceled.
+    return NS_ERROR_FAILURE;
   }
+
+  MOZ_ASSERT(bytesRead == aCount,
+             "AppendToSourceBuffer should consume everything");
+
   return rv;
 }
 
diff --git a/image/SourceBuffer.h b/image/SourceBuffer.h
index 64727e65e..6f2c74d33 100644
--- a/image/SourceBuffer.h
+++ b/image/SourceBuffer.h
@@ -174,6 +174,13 @@ public:
     return mState == READY ? mData.mIterating.mNextReadLength : 0;
   }
 
+  /// If we're ready to read, returns whether or not everything available thus
+  /// far has been in the same contiguous buffer.
+  bool IsContiguous() const {
+    MOZ_ASSERT(mState == READY, "Calling IsContiguous() in the wrong state");
+    return mState == READY ? mData.mIterating.mChunk == 0 : false;
+  }
+  
   /// @return a count of the chunks we've advanced through.
   uint32_t ChunkCount() const { return mChunkCount; }
 
diff --git a/image/decoders/nsWebPDecoder.cpp b/image/decoders/nsWebPDecoder.cpp
index 4f3cc8b2a..3181e3a3a 100644
--- a/image/decoders/nsWebPDecoder.cpp
+++ b/image/decoders/nsWebPDecoder.cpp
@@ -144,6 +144,10 @@ nsWebPDecoder::UpdateBuffer(SourceBufferIterator& aIterator,
 
   switch (aState) {
     case SourceBufferIterator::READY:
+      if(!aIterator.IsContiguous()) {
+        //We need to buffer. This should be rare, but expensive.
+        break;
+      }
       if (!mData) {
         // For as long as we hold onto an iterator, we know the data pointers
         // to the chunks cannot change underneath us, so save the pointer to